In the field of research and industry with biological and chemical reactions as the basic experiment form, in order to obtain optimal results or products, a great number of reaction parameters are screened on a large scale, or multiple detections of different components of a sample are carried out. As the quantity of the required reactions is far beyond that of the reactions operated manually, an automatic parallel processing system for multiple reactions becomes a standard technical tool for this application.
In most applications, most macro-reaction parameters of all the reactions such as temperature and pressure are coincident (they may be time-varying), and the difference between the reactions mainly lies in the chemical substances taking part in reactions. Especially for a large number of biomedical detection applications, different indexes of a sample are determined by adding different reactants into a reaction system. So under many conditions, the parallel processing system for multiple reactions mainly solves the problems of how to add and isolate components of different reactions.
Currently, one known form of such detection device is a microtiter plate/microwell plate. It basically has a solid flat plate with a plurality of wells, and each well on the plate has a unique mark, and is used for storing a sample solution to be detected. For multiple reactions, the general practice is to add different reaction solutions into different wells. As the solution in each well is physically isolated, the reaction processes (hence their products or signals) do not interfere with each other, the end-point results of all the reactions may be read by a special detection instrument (or the entire reaction process is real-time monitored), and accordingly, this device may realize the parallel processing of multiple reactions.
But the defects of the microtiter plate/microwell plate at least lie in:
First, low reaction throughput. According to the general technical standards, a typical microtiter plate may have 6, 24, 96, 384 or 1536 wells. That is, a single microtiter plate maximally performs 1536 parallel reactions. For a classic microtiter plate/microwell plate, to increase its throughput may be achieved just by using much more microtiter plates/microwell plates, but higher cost of the microtiter plate/microwell plate results in high detection cost.
Second, large sample consumption. When the existing microtiter plate/microwell plate is used for detection, each well generally needs a solution volume of tens to hundreds microliter (μL). This results in substantial difficulty in many biological or medicinal researches whose samples are extremely limited and too valuable to be disposed in a single-use manner.
Third, complicated sample-adding technology. For the microtiter plate/microwell plate, sample adding refers to the process of adding a certain volume of sample solution into each microwell. As the design of the microtiter plate is unbeneficial for locating a certain microwell in the array by a human operator, mistakes are easily made during manual adding of samples into a microtiter plate with 96 wells or above, so an automatic liquid transferring system is generally needed. However, this sample adding robot specially made for the microtiter plate is generally expensive and operated complicatedly, thus the cost of the entire detection process is increased.
Forth, high fabrication cost. One microtiter plate/microwell plate meeting the industrial standards has strict requirements for the properties such as mechanical, optical, chemical and surface properties, etc., and the structural size of the microtiter plate/microwell plate must guarantee enough processing precision on the premise of meeting above requirements. These lead to no significant reduction of its fabrication cost in the long-term application history of the microtiter plate/microwell plate.
As mentioned above, under many conditions, the difference between multiple reactions lies in the substances taking part in the reactions; one feasible technical approach is to store unique components of each reaction in independent reaction vessels (labeled or recorded for differentiation) but to add the same components in all the reaction vessels. The U.S. Company BioTrove developed an OpenArray® multi-well plate based on this technical approach, structurally, the OpenArray plate is a solid flat plate with multiple cylindrical wells, and the number of its wells are about 2000-3000. The inner surfaces of all the wells are chemically treated to be hydrophilic, but two opposite surfaces of the flat plate connected by the wells are hydrophobic. A matched automatic sample adding system is used to add unique reaction components into each well in advance. But the common reaction components to all the reactions (for example, the sample solution to be detected) may be added into all the wells once by a special sample adding instrument. After sample adding is finished, the reaction in each well depends on the reaction components added in advance, thus the parallel processing of multiple reactions is achieved. Compared with the traditional microtiter plate/microwell plate, the OpenArray detection flat plate has a plurality of advantages, for example, the manufacture process is simple, the limitations on the light transmission performance of the plate material are relatively loose, adding samples by directly immersing the entire plate in the sample solution and then taking the plate out allows no use of an expensive special sample adding device, etc. But when used for high-throughput detection, the OpenArray technique also has some defects, for example, adding all the 3072 wells needs about 100 μL sample solution calculated according to about 33 nanoliters (nL) of liquid per well, and its sample consumption is larger. Furthermore, above results are obtained by using a special microfluid sample adding device developed for the OpenArray flat plate. Sample adding by the immersion method needs tens to hundreds of milliliters (mL) of solution. In addition, adding unique compound components of each reaction in advance into micro-wells is difficult, specially speaking, accurately adding these compounds into the micro-wells needs accurately adjusting the position of a spotting needle, which leads to expensive fabrication cost of the sample adding system; and the design of the throughput is limited by the precision of the sample pre-adding system. Meanwhile, the array of micro-wells must be machined precisely (even smaller position deviation caused by technical errors will lead to difficult spotting), thereby increasing the cost in a further aspect.
The U.S. Company Fluidigm developed another Dynamic Array or Digital Array integrated fluid circuit for dispensing and adding of sample solutions. With this technique precise automatic control of high-throughput detection process may be achieved. The throughput range of its product lines at present are approximately 2000-37000 parallel reactions/chips, and the volume range of the samples required is 10-0.85 nL per reaction, accordingly, its maximal throughput and minimal sample volume required by a single reaction are superior to those required by the OpenArray plate. However, the microfluid chip has complicated design and extremely high requirements for manufacture process. Moreover, the assay procedure requires expensive and dedicated instrumentation such as special sample adding and detection devices.